Hydraulic mechanism



Aug. 14, 1962 c. A. L. RUHL 3,049,101

HYDRAULIC MECHANISM Filed April 5, 1961 S E 3 *s S & BY K @mi zawd $1M,

ATTORNEYS United States Patent Ofilice 3,M9, l hi Patented Aug. 14, 1962 3,049,101 HYDRAULIC MECHANISM Charles A. L. Rubi, Kalamazoo, MiclL, assignor to The New York Air Brake Company, a corporation of New Jersey Filed Apr. 3, 1961, Ser. No. 100,257 3 Claims. (Cl. 121-46.5)

This invention relates to hydraulic systems for controlling double-acting differential area piston motors.

In systems of this kind, the piston motor frequently is under the control of a four-position directional control valve. These valves are provided with an inlet port which is connected with a pump, an exhaust port which is connected with a reservoir or sump, and a pair of motor ports which are connected with the opposite sides of the piston motor. The control valve has a neutral or hold position in which each motor port is isolated from the other three ports; a raise position in which the inlet port is isolated from the exhaust port but is connected with one motor port, while the exhaust port is connected with the other motor port; a lower position in which the inlet and exhaust ports are isolated from each other and the connections between these ports and the two motor ports are reversed; and a float position in which all four ports are interconnected.

This type of system is used frequently in loaders for controlling the hoist motor which raises and lowers the bucket. In these installations, the lower position is used for digging whereas the float position is used to elfect rapid dropping of the bucket from a raised position. It has long been a problem in this field to maintain the expanding side of the hoist motor liquid-filled during the bucket-dropping operation. An obvious means of preventing cavitation in that motor is to restrict severely the flow from the contracting side of the motor to the sump to thereby build up a back pressure adequate to force fluid into the expanding side, but this solution limits the rate of drop of the bucket.

The object of this invention is to provide means for maintaining the expanding side of a double-acting piston motor liquid-filled without unduly limiting the rate of movement of the motor. The invention is based upon the realization that one of the factors aggravating the cavitation problem is the fact that the oil expelled from one side of the motor must travel twice the distance between the motor and the control valve before reaching the other side of the motor. Since, in some cases, this path is extremely long, rather high back pressures are required to move the oil through the path at the necessary rate. This factor is minimized by the present invention through the provision of a valving device that can be mounted on or at least near the piston motor and which, in response to the pressures in the conduits extending between the control valve and the motor, automatically establishes a direct replenishing path between the opposite sides of the motor when the directional control valve is in the float position. This path is in parallel flow relation with, and thus provides a by-pass around, the normal replenishing path established in the directional control valve so it shortens greatly the length of the flow path travelled by the replenishing oil flowing from the contracting to the expanding side of the motor. Since the length of the path is decreased materially, a smaller back pressure is required to move the oil into the expanding side along that path. As a result, flow from the contracting side of the motor to the sump need not be severely restricted and, consequently, rate of movement of the motor is not limited.

The valving device of the present invention is characterized by the provision of positive seal means in the passage connecting the side of the piston motor which normally sustains the load with one of the motor ports of the directional control valve. These positive seal means serve to isolate the directional control valve, when it is in its hold position, from the high load pressure developed in the motor. As a result of the protection afforded by the positive seal means, leakage in the control valve and drifting of the motor are avoided. Since the necessity for special sealing means in the directional control valve is eliminated, the advantage is presented that the control valve plunger may be mounted merely with a slide fit in its bore, thus simplifying and economizing the manufacture and assembly of the valve. Furthermore, the positive seal means serves to prevent dropping of the load when the control valve is shifted to its raise" position and hence the use of the customary check valve in the control valve plunger is obviated.

According to another feature of the invention, the hy-pass replenishing path includes a normally-closed poppet valve which is operable by the control element of the directional control valve. The poppet valve includes a valve member having a pair of opposed reaction surfaces which are subjected, respectively, to the pressures of fluid in two separate chambers connected by a passage containing a flow restriction. Means, operable by the control element, are provided for establishing a pressure differential between the two chambers to effect movement of the valve member and opening of the by-pass replenishing path when the control element is in its float position.

The preferred embodiment of the invention is described herein in conjunction with the accompanying drawing whose single figure is a schematic diagram showing the valving device and a typical system in which it is used.

Referring to the drawing, the hydraulic system includes a double-acting differential area piston motor 11 which is under the control of a four-position directional control valve 12. The valve shown in US. Patent 2,916,050, granted December 8, 1959, is one example of a suitable directional control valve. The control valve 12 comprises a housing having an inlet port connected with the pump 13 via conduit 14, an exhaust port connected with sump 15 via conduit 16, and a pair of motor ports connected with conudits 17 and 18, respectively. Communication between these ports is controlled by the valve plunger 19 which is axially shiftable between the positions illustrated by the letters L, H, R and F to establish, respectively, the lower, hold, raise and float conditions referred to above.

Interposed between motor 11 and control valve 12 is a valving device 21 having a housing 2.2 containing ports 23 and 24 that are connected with the motor ports of control valve 12 via conduits 18 and 17, respectively, and ports 25 and 26 that are connected with the opposite sides of motor 11 by conduits 27 and 28. The housing 22 contains a through bore 29 having enlarged counterbore portions 31 and 32 which receive the sleeves 33 and 34, respectively, that are held in place by threaded plugs 35 and 36. At its right-hand end, the sleeve 33 is provided with an annular valve seat 37 and with a pair of dia metrically-opposed radial passages 38, 39. Slidable in sleeve 33 is-a poppet valve 41 carrying a chamfered valving surface 42 and containing an axial bore 43 and a radial passage 44. Valve member 41 is partially encircled by a C-shaped wire 46 having a bent end portion that extends into and restricts passage 44. Coil spring 47, whose opposed ends are seated between the surface 48 of plug '35 and the end wall of counterbore 45, normally closes valve 41 on its seat 37.

At its left end, sleeve 34 is provided with an annular seat 53 and with a pair of diametrically-opposed radial passages 54 and 55. Slidable in sleeve 34 is a check valve member 56 carrying chamfered surface 57 and containing axial bore 58 and radial passages 59. Coil spring 61, whose opposed ends are seated on plug 36 and the end wall of counter-bore 62, normally closes valve 56 upon seat 53.

The housing 22 is similarly provided with a second through bore 71 having, at each end, enlarged counterbore portions 72 and 73. Sleeve 74 is secured in counterbore 72 by threaded plug 75 and is provided, at its righthand end, with an annular seat 76 and with a pair of diametrically-opposed radial passages 77 and 78. Mounted in sleeve 74 is the valve member 79 carrying a chamfered surface 81 and containing bore 82 and radial passages 83. Member 7 9 is biased to the right into engagement with seat 76 by coil spring 84.

Reciprocable plunger 91 is mounted in counterbore 73 and is provided, at one end, with a first axial extension 92 arranged to engage check valve member 79 and, at the other end, with a second axial extension 93 arranged to engage stop plug 94. Extension 93 and plug 94 limit the extent to which the plunger 91 is shiftable to the right. Plunger 91 is shiftable to the left to open check valve member 79 by means of extension 92.

Communication between port 23 and the second bore 71 is provided by housing chamber 95, and communication between port 25 and sleeve passages 37, 38, 77 and 78 is afforded by housing chamber 96. Communication between ports 24 and 26 and sleeve passages 54 and 55 is afforded by housing chamber 97.

As illustrated diagrammatically in the drawing, a valve housing 101 is connected with the housing of directional control valve 12 and includes chambers 102 and 103 separated by transverse wall 104. Wall 104 is provided with an opening which defines valve seat 105. Chamber 102 is connected with sump via port 106 and conduit 107, and chamber 103 is connected with plug passage 49 via port 108 and conduit 109. Poppet valve member 111 is mounted in chamber 103 and is biased to the left into engagement with seat 105 by spring 112.

The right-hand end of plunger 19 extends into chamber 102 and is provided with axial extension 19' arranged to engage poppet valve member 111. When plunger 19 is shifted to the right to its float position, extension 19' engages member 111 and moves the same to the right to open the passage through valve seat 105. Chamber 96 then is connected with sump via the pilot path comprising passages 38, 39 and 44, bore 43, passage 49, conduit 109, port 108, seat 105, chamber 102, port 106 and conduit 107.

During operations, the motor 11 is connected with the load (for example, the bucket of a loader) in such a manner that the load imposed on the motor tends to contract piston chamber 11a. If plunger 19 is shifted to the left to its raise" position, a flow path is established in valve 12 to connect conduit 14 with conduit 18 and to connect conduit 17 with conduit 16. Fluid is fed from pump 13 to piston chamber 11a via conduit 14, valve 12, conduit 18, port 23, chamber 95, bore 71, check valve 79, passages 77 and 78, chamber 96, port and conduit 27. Valve 111 is maintained in its closed position by spring 112 and the pressures in chambers 96 and 103 are equalized via passages 38 and 39, restricted passage 44, bore 43, passage 49, conduit 109 and port 108. The piston rod chamber 11b is connected with sump 15 via conduit 28, port 26, housing chamber 97, port 24, conduit 17, valve 12 and conduit 16. The high pressure fluid delivered by the pump 13 to motor chamber 11a is effective to move the piston to the right against the load.

When valve plunger 19 is shifted to the right to its hold position, conduits 17 and 18 are blocked so that no fluid flows to or from either one. The pressures in chambers 95 and 96 are equalized and check valve 79 is closed by spring 84. The motor 11 is now hydraulically locked and the load carried by the motor maintains the fluid in chamber 11a, conduit 27 and chamber 96 under positive pressure. It is important to note that check valve 79 constitutes a positive seal for isolating this load pressure from the valve 12 with the result that the need for high pressure sealing means with plunger 19 is eliminated.

If the plunger 19 is now shifted to the right to its lower position, the connections between the motor ports are reversed and pump 13 is connected with the piston rod chamber 11b via conduit 14, valve 12, conduit 17, port 24, chamber 97, port 26 and conduit 28. Chamber 96 communicates with motor chamber 11a via port 25 and conduit 27, and chamber is connected with sump via port 23, conduit 18, valve 12 and conduit 16. Since the pressure in chamber 97 exceeds the pressure in chamber 95, plunger 91 is shifted to the left to open check valve 79 and thereby vent motor chamber 11a. The piston now moves to the left under the action of the load and the pressure of the fluid in motor chamber 11b. Poppet valves 41 and 111 remain in their closed positions.

If valve plunger 19 is now shifted further to the right to its float position, conduits 14, 16, 17 and 18 are interconnected through valve 12 and the pressures in chambers 95 and 97 are equalized. Spring 84 now closes valve '79. Movement of plunger 19 causes extension 19 to open poppet valve 111 in the pilot path from chamber 96 to sump 15. Due to the restriction in passage 44, flow of fluid along the pilot path creates a large pressure differential between chambers 96 and 50 that is effective to shift valve member 41 to the left against the bias of spring 47. The fluid expelled from the contracting chamber 11a of piston motor 11 now may flow to the expanding chamber 11b through conduit 27, port 25, passages 38 and 39, bore 29, past check valve 56, and through chamber 97, port 26 and conduit 28. Since the motor 11 employs a differential area piston, the quantity of fluid displaced from the contracting chamber 11a is greater than that required to maintain the expanding chamber 11b liquidfilled. The excess fluid is diverted to sump 15 through chamber 97, port 24, conduit 17, valve 12 and conduit 16. It is contemplated that the valving device 21 will be mounted on or very near motor 11, and, therefore, the flow resistance afforded by conduit 17 will produce a back pressure in chamber 97 suflicient to maintain chamber 11b liquid-filled.

If plunger 19 is now shifted to the left to its lower position, valve member 1 11 closes and flow through the pilot path ceases. As a result, the pressures in chambers 50 and 96 again equalize, thereby permitting spring 47 to shift valve member 41 toward its seat to block the replenishing path through bore 29. Fluid now is transmitted to and from the opposite sides of motor 11 in the manner described above.

When plunger 19 is shifted to the left to the hold position, the motor 11 is again hydraulically locked and the check valve 79 closes to isolate the load pressure established in chamber 11a from the valve 12 as described above.

As stated previously, the drawing and description relate only to the preferred embodiment of the invention. Since many changes can be made in the structure of this embodiment without departing from the inventive concept, the following claims should provide the sole measure of the scope of the invention.

What is claimed is:

1. In combination, a double-acting differential area piston motor; a four-position control valve including a housing provided with first and second motor ports and a movable control element having hold and float positions; a first conduit connecting said first motor port with the piston end of said piston motor; a second conduit connecting said second motor port with the rod end of said piston motor; a transverse conduit connecting said first and second conduits; a check valve in that portion of said first conduit between said transverse conduit and said first motor port and arranged to prevent fluid flow from said piston end to said first motor port; pressure-responsive means for opening said check valve when the pressure in said second conduit is greater than the pressure in that portion of said first conduit between the check valve and said first motor port; auxiliary valve means normally closing said transverse conduit; and means responsive to the position of said control element for opening said auxiliary valve means when said control element is in its float position.

2. The combination defined in claim 1 in which said auxiliary valve means comprises a bypass valve in said transverse conduit, and a second check valve in said transverse conduit between said second valve and said second conduit and arranged to prevent flow from said second conduit to said transverse conduit; and in which said position-responsive means is operable to open and close the bypass valve.

3. The combination defined in claim 2 in which said bypass valve comprises a housing having a valve seat, a movable valve member in said housing, and spring means reacting between the housing and said valve member and biasing the valve member toward its seat; and in which said position-responsive means comprises a sump, a venting conduit connecting said first conduit with the sump, flow-restricting means in said venting conduit, and a normally-closed pilot valve in said venting conduit, said pilot valve being arranged to be opened by said control element when said control element is in the float position, the valve member of said bypass valve having a pair of opposed reaction surfaces which are subjected to the fluid pressure in that portion of said first conduit between the first check valve and the piston end of the piston motor and to the fluid pressure portion of said venting conduit which is downstream of the restriction means, respectively.

References Cited in the file of this patent UNITED STATES PATENTS 2,267,284 Livers Dec. 23, 1941 2,367,682 Kehle Jan. 23, 1945 2,980,136 Krehbiel Apr. 18, 1961 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. $049,101 August 14, 1962 Charles A., L. Ruhl It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6,, line 12 after "pressure" insert in that Signed and sealed this 18th day of December 1962 (SEAL) Attest:

ERNEST w. SWIDER DAVID L LADD Attesting Officer Commissioner of Patents 

